1. Field of the Invention
The present invention relates to a rotor phase/speed estimating device that estimates a phase (i.e., a position) and a speed of a rotor without having to use a position/speed sensor (i.e., in a sensor-less manner). The rotor phase/speed estimating device is preferably used in a drive control device in an AC motor in which a rotor shows a salient pole characteristic with respect to a high-frequency current having a frequency higher than a drive frequency (e.g., a permanent-magnet synchronous motor including a permanent magnet arranged in a rotor, a wound-rotor type synchronous motor, a synchronous reluctance motor, a hybrid field-magnet type synchronous motor including a permanent magnet and a field winding arranged in a rotor, an induction motor, etc.).
2. Description of the Related Art
High-performance control of an AC motor can be achieved by a so-called vector control method. Information on a phase of a rotor or a speed thereof as a derivative of the phase is needed in the vector control method. In the past, use has been made of a position/speed sensor such as an encoder or the like. However, the use of this kind of position/speed sensor is not desirable from the view point of reliability, axial volume, sensor cable arrangement, and cost. Research and development have long been conducted regarding a so-called sensor-less vector control method requiring no position/speed sensor.
As a dominant sensor-less vector control method, there has heretofore been developed and reported a variety of high-frequency voltage injection methods that estimate a rotor phase or the like by forcibly injecting a high-frequency voltage having a frequency higher than a drive frequency to a motor and then detecting and processing a high-frequency current as a response thereto.
A rotor phase to be estimated may be set as an arbitrary position of a rotor. If the rotor shows a salient pole characteristic, it is typical that one of a negative salient pole phase and a positive salient pole phase of the rotor is selected as the rotor phase. As is well-known to those skilled in the art, an electric phase difference between the negative salient pole phase and the positive salient pole phase is nothing more than ±Π/2(rad). If one of the negative salient pole phase and the positive salient pole phase is identified, the other becomes automatically known. In view of the above, the negative salient pole phase of the motor will be used as a rotor phase in the following description unless explicitly mentioned otherwise.
A high-frequency voltage injection method in a broad sense is composed of the combination of a high-frequency voltage injection method in a narrow sense for determining a generation method of a high-frequency voltage to be injected and a phase estimating method for processing a high-frequency current as a response to the high-frequency voltage injected and determining generation of a rotor phase estimate value. As the high-frequency voltage is injected in the high-frequency voltage injection method in a narrow sense, an alternating high-frequency voltage having a zero direct current component and a fixed high frequency is often used. A sinusoidal form and a rectangular form are known as the representative signal forms of the alternating high-frequency voltage.
As the high-frequency voltage injection method in a narrow sense for applying a sinusoidal high-frequency voltage, there are known a generalized elliptical high-frequency voltage injection method, a fixed circular high-frequency voltage injection method (e.g., a fixed-amplitude circular high-frequency voltage injection method), a constant-amplitude non-rotational high frequency voltage injection approach, and so forth. In the event that a sinusoidal high-frequency voltage having a high frequency ωh is injected on a γ-δ semi-synchronous coordinate system having a coordinate speed ωγ (a coordinate system composed of a γ axis aiming at getting synchronized with a rotor phase with a fixed phase difference represented by a zero phase difference and a δ axis orthogonal to the γ axis), the sinusoidal high-frequency voltage injected by the generalized elliptical high-frequency voltage injection method is expressed by the following equation. In the subject application, signals relating to a high-frequency voltage and a high-frequency current will be clearly specified by attaching a subscript h thereto.
                                              ⁢                  Formula          ⁢                                          ⁢          1                                                                                                        v                              1                ⁢                h                                      =                                          V                h                            ⁡                              [                                                                                                                              (                                                      1                            +                                                          K                              ⁢                                                                                                ω                                  γ                                                                                                  ω                                  h                                                                                                                                              )                                                ⁢                        cos                        ⁢                                                                                                  ⁢                                                  ω                          h                                                ⁢                        t                                                                                                                                                                          (                                                      K                            +                                                                                          ω                                γ                                                                                            ω                                h                                                                                                              )                                                ⁢                        sin                        ⁢                                                                                                  ⁢                                                  ω                          h                                                ⁢                        t                                                                                            ]                                              ;                                                                                          V                    h                                    =                  const                                                                                                                          ω                    h                                    =                  const                                                                    ,                              0            ≤            K            ≤            1                    ;                      K            =            const                                              (        1        )            
The sinusoidal high-frequency voltage injected by the fixed circular high-frequency voltage injection method is expressed by the following equation.
                    Formula        ⁢                                  ⁢        2                                                                                  v                          1              ⁢              h                                =                                    V              h                        ⁡                          [                                                                                          cos                      ⁢                                                                                          ⁢                                              ω                        h                                            ⁢                      t                                                                                                                                  sin                      ⁢                                                                                          ⁢                                              ω                        h                                            ⁢                      t                                                                                  ]                                      ;                                                                              V                  h                                =                const                                                                                                          ω                  h                                =                const                                                                        (        2        )            
The sinusoidal high-frequency voltage injected by the linear high-frequency voltage injection method is expressed by the following equation.
                    Formula        ⁢                                  ⁢        3                                                                                  v                          1              ⁢              h                                =                                    V              h                        ⁡                          [                                                                                          cos                      ⁢                                                                                          ⁢                                              ω                        h                                            ⁢                      t                                                                                                            0                                                              ]                                      ;                                                                              V                  h                                =                const                                                                                                          ω                  h                                =                const                                                                        (        3        )            
As explicitly specified in an unambiguous manner using equations (1) through (3), the signals of individual vector components in the respective high-frequency voltages have a sinusoidal form expressed by a trigonometric function such as a cosine function or a sine function. In this regard, the variable of the trigonometric function is ωht (i.e., a time integration value of the high frequency ωh). That is to say, the variable of the trigonometric function is expressed by the following equation.Formula 4θh=∫0tωhdτ=ωht  (4)
The sinusoidal high-frequency voltages are not limited to equations (1) through (3) but may be many different values including the combinations of equations (1) through (3). For example, the following high-frequency voltage can be obtained by combining equations (2) and (3).
                    Formula        ⁢                                  ⁢        5                                                                                                v                              1                ⁢                h                                      =                                          V                h                            ⁡                              [                                                                                                                              (                                                      1                            +                            K                                                    )                                                ⁢                        cos                        ⁢                                                                                                  ⁢                                                  ω                          h                                                ⁢                        t                                                                                                                                                K                        ⁢                                                                                                  ⁢                        sin                        ⁢                                                                                                  ⁢                                                  ω                          h                                                ⁢                        t                                                                                            ]                                              ;                                                                                          V                    h                                    =                  const                                                                                                                          ω                    h                                    =                  const                                                                    ,                              0            ≤            K            ≤            1                    ;                      K            =            const                                              (        5        )            
The high-frequency voltage of equation (5) can be obtained by simplifying the high-frequency voltage of equation (1), namely by forcibly making ωγ equal to zero.
Referring to the expression methods of the sinusoidal high-frequency voltage, the rectangular high-frequency voltage can be expressed using the following signum function sgn(•).
                                              ⁢                  Formula          ⁢                                          ⁢          6                                                                                                        v                              1                ⁢                h                                      =                                          V                h                            ⁡                              [                                                                                                                              (                                                      1                            +                            K                                                    )                                                ⁢                                                  sgn                          ⁡                                                      (                                                          cos                              ⁢                                                                                                                          ⁢                                                              ω                                h                                                            ⁢                              t                                                        )                                                                                                                                                                                                  K                        ⁢                                                                                                  ⁢                                                  sgn                          ⁡                                                      (                                                          sin                              ⁢                                                                                                                          ⁢                                                              ω                                h                                                            ⁢                              t                                                        )                                                                                                                                              ]                                              ;                                                                                          V                    h                                    =                  const                                                                                                                          ω                    h                                    =                  const                                                                    ,                              0            ≤            K            ≤            1                    ;                      K            =            const                                              (        6        )            
In the rectangular high-frequency voltage of equation (6), just like the sinusoidal high-frequency voltage, a DC component does not exist and becomes zero.
In order to apply the high-frequency voltage, a stator voltage target value is composed by superimposing and adding a high-frequency voltage target value to a drive voltage target value. The stator voltage target value thus composed is inputted to a power converter (inverter). Thus, the high-frequency voltage can be injected to a motor. The high-frequency voltage injection method in a narrow sense referred to in the present invention is a method for applying the high-frequency voltages as expressed by equations (1) through (6). The high-frequency voltages have a feature that “the fundamental wave component thereof describes an elliptical locus on a γ-δ semi-synchronous coordinate system”. In general, an ellipse differs in the ratio of a minor axis to a major axis. In the present invention, a circular locus is treated as an elliptical locus in which the ratio of a minor axis to a major axis is equal to 1. Similarly, a linear locus is treated as an elliptical locus in which the ratio of a minor axis to a major axis is equal to 0.
As the high-frequency voltage is injected to an AC motor, a high-frequency current is generated in response to the high-frequency voltage. In an AC motor showing a salient pole characteristic with respect to a high-frequency current, the high-frequency current is affected by the salient pole characteristic. Thus, the high-frequency current has salient pole phase information, i.e., rotor phase information. Desired rotor phase information can be detected by processing the high-frequency current containing the rotor phase information.
The stator current detected at a stator terminal of an AC motor includes a drive current having a drive frequency and a high-frequency current having a high frequency. In order to detect the rotor phase information from the high-frequency current, it is usually required that only the high-frequency current is separated and detected from the stator current prior to the detecting the rotor phase information. In the past, it was generally understood that filtering, one representative dynamic processing, is used to separate and detect only the high-frequency current from the stator current (see Japanese Patent No. 4178834, Japanese Patent Application Publication No. 2007-185080, Japanese Patent Application Publication No. 2009-171680, Japanese Patent Application Publication No. 2009-273254, Japanese Patent Application Publication No. 2009-273283, and Y. Chen, L. Wang and L. Kong: “Research of Position Sensor-less Control of PMSM Based on High Frequency Signal Injection”, Proc. Of International Conference of Electrical Machines and Systems (ICEMS 2008), pp. 3973-3977 (2008-10)).
Considering only the separation and detection of the high-frequency current from the stator current, it is natural to use a filter (a highpass filter or a bandpass filter) in the separation and detection of the high-frequency current. In particular, if the frequency of the high-frequency current to be separated and detected is known and fixed, it is even rational to use the filter. However, if the stable operation of an estimating system is taken into account, it is not necessarily easy to introduce a filter for separation and detection of the high-frequency current into the estimating system. For example, in order to separate and detect a desired high-frequency current from the stator current through the use of a bandpass filter with no variation such as lag and advance of a phase, particularly in order to separate and detect the desired high-frequency current while preventing mixture of other frequency components, it is required to narrow the bandwidth of the bandpass filter. However, the narrow bandwidth tends to make the estimating system unstable. On the contrary, if the stability of the estimating system is considered important, it is necessary to broaden the bandwidth. However, the broad bandwidth tends to simultaneously introduce other components than the high-frequency current having a specified frequency. This makes it difficult to perform estimation with increased accuracy.
As set forth in detail in Y. Chen, L. Wang and L. Kong: “Research of Position Sensor-less Control of PMSM Based on High Frequency Signal Injection”, Proc. Of International Conference of Electrical Machines and Systems (ICEMS 2008), pp. 3973-3977 (2008-10), the design of a bandpass filter for separation and detection of a high-frequency current was carried out by a trial-and-error method in the past. Thus, a great deal of time and effort is needed in appropriately designing the bandpass filter (see Y. Chen, L. Wang and L. Kong: “Research of Position Sensor-less Control of PMSM Based on High Frequency Signal Injection”, Proc. Of International Conference of Electrical Machines and Systems (ICEMS 2008), pp. 3973-3977 (2008-10)). Moreover, each time when the high frequency of the high-frequency voltage injected is changed, it is necessary to redesign the bandpass filter through another time-consuming trial-and-error method (see Y. Chen, L. Wang and L. Kong: “Research of Position Sensor-less Control of PMSM Based on High Frequency Signal Injection”, Proc. Of International Conference of Electrical Machines and Systems (ICEMS 2008), pp. 3973-3977 (2008-10)).
If the highpass filter is used in separating and detecting the high-frequency current, it is usual that the detected high-frequency current undergoes a phase advance due to unavoidable properties of the highpass filter. This phase advance makes it difficult to correctly perform phase estimation. In addition, components beyond the frequency of the high-frequency current are simultaneously mixed into the high-frequency current. This makes it difficult to perform estimation with increased accuracy.
When estimating the phase or speed of a rotor, it is necessary to pay attention even to a positive correlation region between a rotor phase and a correlation signal correlated to the rotor phase. By a narrow positive correlation region, it is meant that the rotor phase is likely to go outside the positive correlation region due to disturbance torque and so forth. Once the rotor phase goes outside the positive correlation region, the stable phase estimation of an estimating system is not guaranteed at all. It is usually impossible to come back to stable estimation once the estimating system fails to perform stable estimation. In the conventional rotor phase estimating methods disclosed in Japanese Patent No. 4178834, Japanese Patent Application Publication No. 2007-185080, Japanese Patent Application Publication No. 2009-171680, Japanese Patent Application Publication No. 2009-273254, Japanese Patent Application Publication No. 2009-273283, and Y. Chen, L. Wang and L. Kong: “Research of Position Sensor-less Control of PMSM Based on High Frequency Signal Injection”, Proc. Of International Conference of Electrical Machines and Systems (ICEMS 2008), pp. 3973-3977 (2008-10), the positive correlation region between a rotor phase evaluated on a γ-δ semi-synchronous coordinate system and a correlation signal correlated to the rotor phase is as narrow as ±Π/4(rad) at most with respect to θγ (see FIGS. 1 through 3B described later).
When estimating the phase or speed of a rotor, it is necessary to pay attention to not only the phase estimating method but also a high-frequency voltage injection method making up an estimating system together with the phase estimating method. However, the prior inventions require a troublesome high-frequency voltage injection means as is noted in Japanese Patent Application Publication No. 2009-171680, Japanese Patent Application Publication No. 2007-185080, Japanese Patent Application Publication No. 2009-171680, Japanese Patent Application Publication No. 2009-273254, and Japanese Patent Application Publication No. 2009-273283, describing that “a rectangular-wave alternating high-frequency voltage consisting of two pulse voltages equal in amplitude and pulse width to each other but differing in polarity from each other is applied to a motor in a plurality of vector directions”.